Among the many functions performed by peptides and proteins in metabolism is the ability to stimulate receptors at cell surfaces to effect intracellular consequences important in maintenance and development of the organism. Peptide and protein hormones interact with receptors specific for them so that the activity of the hormone is felt on designated cells exhibiting these receptors. The insulin receptor is present on virtually all cells and at high concentrations on the cells of the liver, skeletal muscles, and adipose tissue. Stimulation of the insulin receptor with insulin is an essential element in carbohydrate metabolism and storage.
Diabetics either lack sufficient endogenous secretion of the insulin hormone (Type I) or have an insulin receptor-mediated signalling pathway that is to some degree resistant to endogenous or exogenous insulin, either through primary or post-translational structural changes, reduced numbers or poor coupling among signaling components (Type II). All Type I diabetics, and many Type II subjects as well, must utilize injection to obtain enhanced activity of the extant insulin receptors, since endogenous insulin can at present be replaced only with an alternative supply of insulin itself, previously isolated from native sources, and now recombinantly produced. While the recombinant production of insulin permits a less immunogenic form to be provided and assures a reliable supply of needed quantities, the necessity to administer the hormone by injection remains, due to the instability of peptides and proteins in the digestive tract. It has long been the goal to substitute for peptide ligands, including insulin, small molecules which are not digested and can be absorbed directly into the bloodstream. However, to date, nonpeptide substances which can exert the effect of insulin on its receptor have eluded discovery.
There have been many instances in which nonpeptide materials have been used to inhibit enzymes whose native substrates are peptides. For example, Brinkworth, R. I. et al. Biochem Biophys Res Comm (1992) 188: 624-630 describe the inhibition of HIV-1 proteinase by various aryl disulfonates. The ability of triazine dyes to bind NADH oxidase from Thermus thermophilus was studied by Kirchberger, J. et al. J Chromatog A (1994) 668:153-164.
It has also been shown that certain nonpeptide components enhance the agonist properties of a peptide hormone. The ability of certain thiazolidinediones such as pioglitazone to enhance adipocyte differentiation by stimulating the effect of insulin has been described by, for example, Kletzien, R. F. et al J Mol Pharmacol (1992) 41 :393-398. These represent a class of potential antidiabetic compounds that act at an unknown site downstream from the insulin receptor itself and enhance the response of target tissues to insulin. Kobayashi, M. Diabetes (1992) 41:476-483. It is now known that most of the thiazolidinediones bind to PPAR.sub.65 thus triggering certain nuclear events that may result in enhanced sensitivity of the target cells to insulin. However, the complete mechanism is still unresolved.
In any event, it has not as yet been possible to utilize simple molecules to provide the effect of a peptide hormone by stimulating receptor activity independently of the peptide hormone binding site.
It has now been found that several aryl di- or polysulfonate compounds which share certain common structural features are able to effect stimulation of the insulin receptor to activate the autophosphorylation activity required for signal transduction. The availability of these compounds permits construction of assays and comparative procedures for evaluating additional candidate compounds as well as the design and synthesis of therapeutics for primary treatment of insulin resistance and diabetics with the appropriate structural features.